The lac operon produces what type of mRNA?

• A. Monocistronic mRNA
• B. Polycistronic mRNA
• C. rRNA
• D. tRNA

Answer: (B)

Polycistronic mRNA is produced by bacterial operons like the lac operon. In this setup, multiple genes are transcribed together into a single mRNA that contains several protein-coding regions. The lac operon has three structural genes—lacZ, lacY, and lacA—whose products participate in lactose metabolism. Because they’re co-transcribed, one mRNA carries the instructions for all three enzymes, and ribosomes can initiate translation at each gene’s start site to produce multiple proteins from the same transcript. This contrasts with monocistronic mRNA, typical in many eukaryotes, where one mRNA usually encodes a single protein. rRNA and tRNA are different types of RNA and are not mRNA. So the lac operon yields polycistronic mRNA.